An electric motor included as a driving source in a mobile body such as a hybrid-type electric vehicle (HEV), an electric vehicle (EV), and an electric railroad vehicle is required to have both advantages of compactness and lightness and of high output. Generally, there is a close relationship between the size of the motor and the cooling efficiency of the motor. When the cooling efficiency of the motor improves, the output of the motor in the same size rises. Thus, various methods for improving the cooling efficiency have been developed such as addition of fins, addition of a dedicated cooling system constituted by a fan and a pump, and addition of a structure capable of enlarging the heat release area.
For example, PTL1 discloses a structure which includes a cooling system constituted by a heat pipe and a radiator. According to this technology, the motor and the radiator are connected with each other via a heat pipe so that heat transmitted via the heat pipe to the radiator can be dissipated from the radiator to the air.